The requirement for any dragline is to move the largest amount of material per unit time, typically measured in tonnes per hour. High productivity achieved at the cost of high or undesirable loads on the dragline will generate increased maintenance costs and downtime so it is therefore important not to overload the bucket of a dragline in order to increase productivity. Research has indicated that the bulk density of blasted material in a dragline pit can vary greatly depending on blast performance, particularly in throw blasts. This variation has a significant effect on bucket size required to achieve desired or optimal payload (thus rated suspended load) as well as the digability of the material.
It is desirable to provide accurate estimates of the bulk density in order to provide the benefits of reliable assessment of dig and blast performance, improved bucket size selection to achieve consistent suspended load targets, and decreased production costs by reduced dragline damage and improved productivity through reduced probability of bucket overloads.
Although work has been done in the past in determining material density in other open pit mining situations such as in excavator buckets or in haul trucks, it is extremely difficult to provide real-time density determination in a dragline bucket due to the difficulty in determining the accurate bucket pose estimation, payload extraction, and filtering. The bucket is attached to free moving ropes and thus the dynamics of the bucket at any point in time are unknown.
The bulk density of the payload material in the bucket of a dragline is typically determined by measuring payload weight and dividing that weight by payload volume. Determination of payload weight is reasonably well known and able to be determined from proprietary products which measure rope lengths and motor currents to determine the load on the dragline hoist ropes at any point in time and hence enable calculation of the weight of the payload in the dragline bucket. The main objective of the present invention is to provide a method of accurately determining the volume of the payload in the bucket during the carry phase of the dragline dig and dump cycle in order to allow real-time calculation of the bulk density of the material in the dragline bucket.